1. Field of the Invention
The present invention relates to the technique of displaying three-dimensional images on a screen, and more particularly, to a three-dimensional graphic processing device for displaying an object on a screen with polygons.
2. Description of the Background Art
In recent years, three-dimensional graphic processing devices to process three-dimensional images at a high speed have been actively developed to output lively and dense images in personal computers and home video game machines. In the three-dimensional graphic device, polygons are used as a basic plotting unit to express an object on the screen, and the number of such polygons to be drawn has increased as the graphics has been denser. In order to improve a drop in the drawing throughput by the increase in the number of polygons, the definition of a series of polygons by Strip and Fan or the like have been widely used.
FIGS. 1A to 2B are diagrams for use in illustration of how a series of polygons are drawn in a conventional three-dimensional graphic processing device. FIG. 1A shows the coordinate definition of the basic polygon, which is represented by first point 110, second point 111 and third point 112. FIG. 1B shows the coordinate value data (x coordinate value, y coordinate value) of first point 110, second point 111, and third point 112 of the basic polygon. Note that the coordinate values (x1, y1) of first point 110, the coordinate value (x2, y2) of second point 111 and the coordinate values (x3, y3) of third point 112 are all defined by absolute coordinate values.
FIG. 2A shows the coordinate definition of a series of polygons continuing to the basic polygon shown in FIG. 1A (hereinafter referred to as xe2x80x9csecond polygonsxe2x80x9d), which is represented by first point 110, the same point from the basic polygon, third point 112, the same point from the basic polygon, and the newly defined fourth point 116. FIG. 2B shows the coordinate value data of first point 110, fourth point 116 and third point 112 in the second polygon. Note that the coordinate values (x4, y4) of newly defined fourth point 116 are also defined by absolute coordinate values.
In drawing the series of polygons as described above, the coordinates of the vertex added at the time of defining the series of polygons are also defined by absolute coordinate values, and therefore the amount of polygon coordinate data and texture mapping coordinate data necessary for drawing are large. Furthermore, color data associated with each vertex is independently defined, which also increases the amount of data. These disadvantages lower the drawing throughput caused by the restriction in the memory access band, which eventually lowers the performance of the three-dimensional graphic processing device as a whole.
It is one object of the present invention is to provide a three-dimensional graphic processing device capable of reducing the vertex data of polygons to be drawn and having an improved drawing throughput, and a method therefor.
Another object of the present invention is to provide a three-dimensional graphic processing device capable of preventing the performance of the device as a whole from being lowered by the restriction of the memory access band width and a method therefor.
A three-dimensional graphic processing device according to one aspect of the invention includes an identifying portion for identifying whether the vertex data of a polygon to be drawn is an absolute value or a relative value, an operation portion for operating to obtain the absolute value of vertex data identified as a relative value by the identifying portion and generation portion for generating data necessary for drawing based on the absolute value of the vertex data obtained by the operation portion.
Since the operation portion operates to obtain the absolute value of vertex data identified as a relative value by the identifying portion, the vertex data of polygons can be expressed by a relative value. As a result the amount of polygon data can be reduced, which improves the drawing throughput. The reduction in the data amount permits the number of access to the memory to be reduced, so that degradation in the performance of the device as a whole caused by the restriction of the memory access band width can be prevented.
A three-dimensional graphic processing method according to another aspect of the invention includes the steps of identifying whether the vertex data of a polygon to be drawn is an absolute value or a relative value, operating to obtain the absolute value of vertex data identified as a relative value and generating data necessary for drawing based on the operated absolute value of vertex data.
Since the absolute value of vertex data identified as a relative value is obtained by operation, the vertex data of a polygon can be expressed by a relative value. As a result, the amount of polygon data can be reduced, which improves the drawing throughput. The reduction in the data amount permits the number of access to the memory to be reduced, so that degradation in the performance of the device as a whole caused by the restriction of the memory access band width can be prevented.